The worst cases – those with limbs missing and severe burns – were put on Black Hawk helicopters to the field hospital, while the less urgent victims travelled by military ambulance, stacked on stretchers in the back.

First stop: the outside triage station, where one soldier groaned as medics cut off his fatigues to discover his organs hanging out of his stomach. (Really, they were condoms filled with Kool-Aid and cocoa, to make the liquid a bit lumpy.) It wasn’t, obviously, a real battle scene – although the American and South Korean soldiers acted as though it was – but rather a two-day medical evacuation drill called Dragon Lift that ended yesterday, part of joint spring military exercises.

They were simulating their response to an artillery attack from Kim Jong Un’s army, on the site of a South Korean military hospital 13km from the border with North Korea and not far from Uijeongbu, the setting for the Korean War television series M.A.S.H.

In the olive-green tents, there was even a decked-out operating theatre, complete with surgeons and an anaesthetist.

Once stabilised, the urgent cases were flown to the US Air Force base at Osan and loaded on stretchers into the back of a Hercules for evacuation to Japan.

The US military still has 28,500 troops in South Korea – a legacy of the Korean War, which left the peninsula physically and ideologically divided – and they operate under the constant refrain that they should be ready to “fight tonight”.

These kinds of exercises helped the two militaries figure out how to work together, said Lieutenant Colonel DJ Kimbler, who was overseeing the field hospital.

“It increases not only our readiness, but it increases the readiness of the alliance and makes us more ready to fight tonight here on the Korean Peninsula,” he said.

Twice a year, the American and South Korean militaries conduct joint exercises to prepare for a North Korean invasion or the sudden collapse of the regime.

But this year, the spring exercises are taking place at a particularly tense time: amid international condemnation of the North’s January nuclear test and February long-range rocket launch.

The exercises – which include computer simulations of surgical strikes against the North Korean leadership – have elicited an angry response from Pyongyang.